Enhanced 1.8 μm emission in Yb3+/Tm3+ co-doped tellurite glass: Effects of Yb3+↔Tm3+ energy transfer and back transfer

- Enhanced J-O parameters: higher degree of covalency of the glass network.
- High Yb3+→Tm3+energy transfer rate with 88.4% efficiency under 982 nm excitation.
- Enhanced Tm3+: 1.8 µm emission on account of reduced vis-upconversion emissions.
- High gain cross-section even under low 60% population inversion over a broad wavelength range.

The ~1.8 μm emission characteristics of Tm3+ by a direct excitation and through an energy transfer process upon sensitization with Yb3+ ions in tellurite glass are reported. The spectroscopic properties of Tm3+ ions have been evaluated by applying Judd-Ofelt theory on the measured absorption spectrum. The obtained intensity parameters, Ω2=7.155×10−20 cm2, Ω4=3.325×10−20 cm2, Ω6=1.278×10−20 cm2 are used to estimate the radiative properties of Tm3+ ions in the present glass host. A ~10 fold enhancement in the Tm3+ 1.8 μm emission observed with 16 fold reduced emission of Yb3+ ions (1008 nm) in co-doped sample on Yb3+ ions excitation illustrates the efficient energy transfer from Yb3+: 2F5/2→Tm3+: 3H5. The energy transfer process assisted by host phonon energy has been discussed by using relevant theoretical models and estimated the energy transfer micro-parameters. Effect of energy back transfer Tm3+→Yb3+ on NIR and upconversion emissions have been discussed. An efficient ~1.8 μm with comparatively higher emission cross-section 1.115×10−20 cm2 on account of reduced upconversion emissions has been achieved in the present tellurite glass.